There are several types of chemically treated lumber such as creosoted lumber and pressure treated lumber. These materials are enjoying an ever increasing level of popularity for use in, for example, guard rails, railroad ties, telephone poles, fences, decks, and retaining walls. These materials are relatively inexpensive to make and use, and they are just as versatile as any other form of wood. They also have enhanced resistance to microbial and to fungal degradation and to water.
However, the increasing popularity of chemically treated lumber has some negative repercussions which are just now being realized. Chemically treating lumber takes a perfectly useable, recyclable, renewable resource and renders it toxic. For example "pressure treated" or "CCA" lumber is treated with a very poisonous chromated copper arsenic material and can not be burned. While CCA lumber can be buried, the leaching of toxic chemicals makes such disposal strategies much less than desirable. Creosoted lumber requires special incinerators. These materials are becoming far more difficult and expensive to dispose of than to use. However, because of the long useful life of these materials, the economic and environmental impact of chemically treated lumber is just beginning to be felt.
A synthetic replacement for chemically treated lumber would have several advantages. It would slow the cutting of hard and soft-wood forests. It would also eliminate the use of hazardous chemicals associated with chemically treated wood and would eliminate the disposal problems associated therewith.
A number of suggestions have been made for producing lumber substitutes to reduce or eliminate the use of chemically treated wood. Some of these materials have been very successful for specific applications. However, to date, none of these materials have been broadly successful, particularly in structurally demanding applications such as railroad ties.
One product available from Trimax of Long Island Incorporated, 2076 5th. Ave., Ronkonkama, N.Y. 11779 is composed of fiberglass distributed in high density polyethylene ("HDPE"). While the fiberglass includes a silane sizing, it is not a coated fiber material as discussed herein.
Another synthetic lumber product is available from Eaglebrook Products Incorporated, 2650 West Roosevelt Rd., Chicago, Ill. 60608. This material is composed of formed HDPE which does not use fibers. The result is a material with low compressive and flexival modulus and a relatively high thermal expansion coefficient.
A rather interesting approach to recycling unwanted tires was proposed by Murray, U.S. Pat. No. 5,238,734. According to Murray, clean and non-crumbling tires are ground into rubber fragments. The fragments, which can include fiberglass and steel belts, are mixed with an epoxy mixture comprising an oxirane-containing resin and an amine-containing hardening agent and molded into railroad ties. While Murray found a use for a growing environmental problem, namely, the proliferation of tires, it would be even more desirable to produce a composite building material constructed almost entirely of recycled materials. This would provide a market for potentially millions of pounds of recycled plastics per year. Therefore, there is certainly room for improvement. See also U.S. Pat. No. 4,137,198; 4,229,497; 4,308,707; 5,053,274 and 5,063,862, all of which relate to plastic-based building materials, some of which may be used for, for example, railroad tie replacements.